Comparison of multiple static segment and sliding window techniques in prostate radiotherapy

Abstract

The purpose of this study is to compare multiple static segment (step and shoot) and sliding window techniques in intensity modulated radiotherapy (IMRT). Ten definitive prostate patients were included in this study. For each patients, two different treatment plans were created. Multiple static segment and sliding window techniques were compared doses in the planning tardet volume (PTV), the organ at risk (OAR) volumes including rectum dose (V50, V35, V25, V20 and V10), bladder dose (V50, V35, V25 and V15), femoral heads mean and maksimum doses, homogeneity index (DHI) and the monitor unit counts (MU) for the treatment. Gamma analysis was performed by using portal dosimetry software in 2 and 3 distance to agreement and 2% and 3% dose difference criteria and their algorithms were compared. Coverage of the planning target volume (PTV) was showed similar results for both sliding window and step and shoot IMRT, however significant differences were found critical organ doses and total monitor unit (MU). Rectum and bladder mean doses for the sliding window and step and shoot plans were 43.37±10.89, 40.03±12.61 and 42.62±10.22, 39.20±12 and the mean MUs were 1014 cGy and 867 cGy respectively. Homogeneity index (HI) was 0.038±0.01 and 0.079±0.001 for SW and MSS techniques. When compared the calculated and measured dose distributions images of the gamma analyses the average result 2/2% and 3/3% were 97.46±1.34, 99.63±0.82 and 98.16± 0.27, 99.33±0.17 for both the sliding window and step and shoot techniques respectively. Two techniques allowed more homogeneous dose distributions in PTV. Considering the dose to organs at risk (OAR) and total MU, MSS technique seems to be advantages than the sliding window. SW and MMS techniques showed comparable results with the respect to gamma analysis.